大兴安岭北段霍洛台铜铅锌矿区花岗闪长岩的岩石成因:地球化学和锆石U-Pb年代学制约

Petrogenesis of granodiorites in Huoluotai Cu-Pb-Zn mining area:constrain from geochemistry and zircon U-Pb geochronology,northern Daxing'anling

黑龙江省大兴安岭地区霍洛台花岗闪长岩的锆石LA-ICP-MS U-Pb年代学表明,霍洛台花岗闪长岩(145 Ma)为早白垩世岩浆侵入产物。元素地球化学组成表明,为一套具埃达克岩特征的高钾钙碱性系列岩石,表现为高SiO_2(65.64%~66.00%)、高K_2O(3.67%~3.77%)、低MgO(0.09%~1.21%)、高Sr含量(814.00×10^(-6)~893.00×10^(-6)),低Yb(0.194×10^(-6)~0.536×10^(-6))和Y(6.38×10^(-6)~7.73×10^(-6)),A/CNK为0.94~0.958,轻重稀土元素分异明显。La/Yb(92.54~245.88)、Th/La(0.17~0.2)、Th/U(4.01~4.84)和Mg~#值(26.70~29.22)等特征显示霍洛台花岗闪长岩为加厚下地壳部分熔融形成。结合区域构造演化背景,认为霍洛台花岗闪长岩为受蒙古—鄂霍茨克构造体系影响下地壳加厚挤压-伸展转换阶段作用产物。

LA-ICP-MS U-Pb zircon geochronology of Huoluotai granodiorite of Daxing＇anling area in Heillongjiang Province shows that Huoluotai granodiorite （145 Ma） results from magmatic intrusion of Early Cretaceous. The composition of elementary geochemistry indicates that it is a set of adakitic rocks characterized by high-K calc-alkaline series, with a high content of SiO2 （65.64%-66.00%） and K2O （3.67%-3.77%）, low MgO （0.09%-1.21%）, high content of Sr （814.00×10^-6-893.00×10^-6）, low Yb （0.194×10^-6 to 0.536×10^-6） and Y （6.38×10^-6 to 7.73×10^-6）, and obvious differentiation of light and heavy rare earth elements （10.1-14）. The characteristics of La/Yb （92.54-245.88）, Th/La （0.17-0.2）, Th/U （4.01-4.84） and Mg# （26.70-29.22） show that the Huoluotai granodiorite was formed by partially melting of the thickened lower crust. Combined with regional tectonic evolution, it is concluded that the Huoluotai granodiorite originated from the transition process of crustal thickening compression to extension under the influence of Mongolia-Okhotsk tectonic system.